Imaging apparatus and interchangeable lens

ABSTRACT

An imaging apparatus includes a plurality of lenses movable along an optical axis, a plurality of drivers configured to drive the plurality of lenses, respectively, and a synchronizm loss detector configured to detect a loss of synchronizm of one of the plurality of drivers. The one of the plurality of drivers is a driver that drives a lens which is heaviest in the plurality of lenses.

BACKGROUND

1. Technical Field

The technical field relates to an imaging apparatus and aninterchangeable lens that include lenses movable in an optical axisdirection. More particularly, the technical field relates to a techniquefor detecting a loss of synchronizm of a motor that drives a lens in animaging apparatus and an interchangeable lens.

2. Related Art

Conventionally, there exists an imaging apparatus that drives a focuslens by a motor. Such a movable lens is driven by, for example, astepping motor. When the movable lens is driven by a stepping motor,there is a problem that, when an external shock is applied to thestepping motor, the stepping motor loses synchronizm and thus cannotmove the movable lens to a desired position. Accordingly, there is aneed to, for example, detect a loss of synchronizm of the steppingmotor, and move the lens to a predetermined reference position when aloss of synchronizm is detected.

For a prior art document pertaining to techniques for detecting a lossof synchronizm of a stepping motor that drives a movable lens, there isJP 07-199033 A. A drive apparatus of a member for driving an opticalsystem described in JP 07-199033A detects a loss of synchronizm of astepping motor, based on the loss of output pulses from aphotointerrupter.

However, resolution of the photointerrupter is not so high, and thus aloss of synchronizm of the stepping motor cannot be detected with highaccuracy by the technique described in JP 07-199033 A.

Meanwhile, for a macro lens that allows for shooting with a focal lengthranging from infinity to 1:1 close up, a plurality of focus lens groupsare allowed to move independently of each other. With such aconfiguration, miniaturization can be achieved while the focal length ischanged greatly.

In such a macro lens, when a loss of synchronizm occurs in even onefocus lens group, even if focus can be achieved, the macro lens cannotrealize it's maximum potential. Hence, detection of a loss ofsynchronizm becomes more important.

To solve the above problem, an imaging apparatus and an interchangeablelens are provided that are capable of detecting a loss of synchronizm ofa motor with high accuracy.

SUMMARY

In a first aspect, an imaging apparatus is provided that includes aplurality of lenses movable along an optical axis, a plurality ofdrivers configured to drive the plurality of lenses, respectively, and asynchronizm loss detector configured to detect a loss of synchronizm ofone of the plurality of drivers. The one of the plurality of drivers isa driver that drives a lens which is heaviest in the plurality oflenses.

In a second aspect, an interchangeable lens mountable to a camera bodyis provided, that includes a plurality of lenses movable along anoptical axis, a plurality of drivers configured to drive the pluralityof lenses, respectively, and a synchronizm loss detector configured todetect a loss of synchronizm of one of the plurality of drivers. The oneof the plurality of drivers is a driver that drives a lens that isheaviest in the plurality of lenses.

It is considered that a driver that drives the heaviest movable lens ismost likely to cause a loss of synchronizm when an external shock isapplied thereto. Hence, according to the above aspects, detection of aloss of synchronizm of a driver for a lens that is more likely to causea loss of synchronizm can be performed, enabling to detect a loss ofsynchronizm with higher accuracy. In addition, since the heaviest lensis generally large and an optical influence exerted thereby is alsolarge, by reliably detecting a loss of synchronizm of the heaviestmovable lens, an optical adverse influence caused by a loss ofsynchronizm can be further reduced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a configuration of an imagingapparatus system according to one embodiment.

FIG. 2 is a diagram showing communication performed between a camerabody and an interchangeable lens.

FIGS. 3A and 3B are a first set of diagrams illustrating the peripheryof a magnetoresistance sensor.

FIGS. 4A and 4B are a second set of diagrams illustrating the peripheryof the magnetoresistance sensor.

FIGS. 5A and 5B are a third set of diagrams illustrating the peripheryof the magnetoresistance sensor.

FIGS. 6A and 6B are a fourth set of diagrams illustrating the peripheryof the magnetoresistance sensor.

FIGS. 7A to 7C are diagrams showing an output voltage from themagnetoresistance sensor.

FIG. 8 is a flowchart illustrating a synchronizm loss detection process.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Preferred embodiment invention will be described below with reference tothe accompanying drawings.

First Embodiment

1. Configuration

FIG. 1 is a block diagram showing a configuration of an imagingapparatus system according to an embodiment. The imaging apparatussystem according to the embodiment is a lens-interchangeable digitalstill camera, and includes a camera body 100 and an interchangeable lens200.

The interchangeable lens 200 is mechanically mounted to the camera body100. When the interchangeable lens 200 is attached to the camera body100, the camera body 100 and the interchangeable lens 200 are alsoelectrically connected to each other. Specifically, power is supplied tothe interchangeable lens 200 from the camera body 100 and communicationbetween the camera body 100 and the interchangeable lens 200 is enabled.The camera body 100 sends an instruction to the interchangeable lens 200to move movable lenses in the interchangeable lens 200. Theinterchangeable lens 200 notifies the camera body 100 of the state ofthe interchangeable lens 200.

The camera body 100 is mounted with a camera body CPU 101 forcontrolling each of units in the camera body 100 and the interchangeablelens 200. The camera body 100 includes an imaging device that convertsan optical signal collected by the interchangeable lens 200 into anelectrical signal, an image processing LSI that converts the electricalsignal outputted from the imaging device into an image signal, a liquidcrystal display that displays the image signal, and a recording mediumthat records the image signal, but these units are not shown in FIG. 1.

The interchangeable lens 200 is mounted with a lens CPU 201 forcontrolling each of units in the interchangeable lens 200 whilecommunicating with the camera body CPU 101. The interchangeable lens 200includes, as an optical system, a first focus lens 202 and a secondfocus lens 203. Although the optical system of the interchangeable lens200 also includes other lenses, they are not shown in FIG. 1. Both thefirst focus lens 202 and the second focus lens 203 are movable along anoptical axis L.

In the interchangeable lens 200 according to the present embodiment, thesecond focus lens 203 is larger and heavier than the first focus lens202. Therefore, when the same shock is applied to them, a driver for thesecond focus lens 203 is more likely to cause a loss of synchronizm thana driver for the first focus lens 202. Hence, in the present embodiment,detection of a loss of synchronizm is performed only on the second focuslens 203 which is heavier. Note that although FIG. 1 shows that thefirst focus lens 202 and the second focus lens 203 are both configuredby a single lens respectively, each of the lenses 202 and 203 may becomposed of a lens group including a plurality of lenses.

The first focus lens 202 is driven in the optical axis L direction by afirst stepping motor 204. A rack which is integrally provided on a framebody that holds the first focus lens 202 engages with a screw providedon a rotating shaft of the first stepping motor 204. With thisconfiguration, when the first stepping motor 204 rotates, the firstfocus lens 202 moves along the optical axis L. It is detected whetherthe first focus lens 202 is in its initial position or not by detectingwhether a part of the frame body that holds the first focus lens 202shields a light receiver of a photointerrupter 206 or not.

The second focus lens 203 is driven along the optical axis L by a secondstepping motor 205. A rack which is integrally provided on a frame bodythat holds the second focus lens 203 engages with a screw provided on arotating shaft of the second stepping motor 205. Therefore, when thesecond stepping motor 205 rotates, the second focus lens 203 moves alongthe optical axis L. A movement of the second focus lens 203 is detectedby a magnet 207 and a magnetoresistance sensor 208 which are integrallymounted on the frame body that holds the second focus lens 203.

The magnetoresistance sensor 208 also detects whether the second focuslens 203 is in its initial position or not. The magnetoresistance sensor208 is a position detection sensor that uses a magnetoresistance effectin which the electrical resistance changes depending on the magneticfield strength. The magnetoresistance sensor 208 is, for example, anAnisotropic Magnetoresistance Sensor (AMR sensor) made of permalloy(Ni—Fe).

The first stepping motor 204 and the second stepping motor 205 aredriven by a drive circuit 209. The lens CPU 201 controls the drivecircuit 209 to move the first focus lens 202 and the second focus lens203 to their respective desired positions, while communicating with thecamera body CPU 101. The lens CPU 201 can determine whether the firstfocus lens 202 is at its initial position or not, from an output fromthe photointerrupter 206. In addition, the lens CPU 201 can determine amovement of the second focus lens 203 and whether the second focus lens203 is at its initial position or not, from an output from themagnetoresistance sensor 208.

Note that the first stepping motor 204 and the second stepping motor 205are examples of drivers for moving the first focus lens 202 and thesecond focus lens 203, respectively, and may be electromagnetic linearmotors or other actuators.

2. Operation

2-1. Communication

FIG. 2 is a diagram showing communication between the camera body 100and the interchangeable lens 200. When the camera body 100 is turned onwith the interchangeable lens 200 being mounted to the camera body 100,the camera body 100 supplies power to the interchangeable lens 200(S11).

The camera body CPU 101 requests authentication information of theinterchangeable lens 200 from the lens CPU 201 (S12). The authenticationinformation of the interchangeable lens 200 includes informationindicating whether the interchangeable lens 200 is mounted or not, andinformation indicating whether any accessory is further attached to theinterchangeable lens 200 or not. The lens CPU 201 sends, as a response,authentication information of the interchangeable lens 200 to the camerabody CPU 101 (S13).

The camera body CPU 101 requests the lens CPU 201 to perform aninitialization operation (S14). In response to the request, the lens CPU201 moves the first focus lens 202 and the second focus lens 203 totheir respective initial positions. The initial positions serve asorigins used to identify the positions of the first focus lens 202 andthe second focus lens 203 after their movement. The lens CPU 201 alsoperforms an initialization operation on other elements (not shown)included in the interchangeable lens 200, such as a diaphragm. When theinitialization operation is completed, the lens CPU 201 sends a responseindicating that the initialization operation has been completed, to thecamera body CPU 101 (S15).

The camera body CPU 101 requests lens data from the lens CPU 201 (S16).The lens data is stored in a memory (not shown) in the interchangeablelens 200. The lens CPU 201 reads lens data from the memory and sends thelens data to the camera body CPU 201 (S17). The lens data includesinformation unique to the interchangeable lens 200, such as the name,F-number, and focal length of the interchangeable lens 200.

When the camera body CPU 101 obtains the lens data of theinterchangeable lens 200 mounted to the camera body 100, the imagingsystem goes into a state where the imaging system is ready to performshooting. After this, the camera body CPU 101 periodically requests lensstate data indicating state of the interchangeable lens 200 from thelens CPU 201 (S18). The lens state data includes positional informationof the first focus lens 202 and the second focus lens 203. The lensstate data also includes information on the aperture value of thediaphragm (not shown), or the like. The lens CPU 201 sends lens statedata to the camera body CPU 101 (S19).

The camera body CPU 101 requests the lens CPU 201 to move lens asrequired (S20). The lens movement request includes a request to moveeach of the first focus lens 202 and the second focus lens 203. The lensmovement request also includes a request to change the aperture value, arequest to move a zoom lens (not shown), or the like. In a response tothe lens movement request, the lens CPU 201 sends information indicatingthat the process by the lens movement request is completed or is inprogress, to the camera body CPU 101 (S21). The camera body CPU 101controls the interchangeable lens 200 while checking the state of theinterchangeable lens 200 based on the lens state data.

2-2. Magnetoresistance Sensor

FIGS. 3A and 3B to 6A and 6B are diagrams illustrating the function ofthe magnetoresistance sensor 208. FIGS. 3A, 4A, 5A, and 6A show a changein state when the second focus lens 203 is moving in a directionindicated by an arrow A in the drawings.

The second focus lens 203 and the magnet 207 are integrally provided.Therefore, when the second focus lens 203 moves in the directionindicated by the arrow A in the drawings, the magnet 207 also moveslikewise. In the magnet 207, north poles and south poles are alternatelyformed at regular intervals. Note that the second stepping motor 205that drives the second focus lens 203 is not shown.

The magnetoresistance sensor 208 includes a first magnetoresistancesensor 208 a and a second magnetoresistance sensor 208 b. Each of thefirst magnetoresistance sensor 208 a and the second magnetoresistancesensor 208 b includes two magnetoresistance elements.

In each of the first magnetoresistance sensor 208 a and the secondmagnetoresistance sensor 208 b, the two magnetoresistance elements areconnected in series. One end of the two magnetoresistance elementsconnected in series is connected to a power supply Vcc and the other endis connected to a ground GND. In each of the first magnetoresistancesensor 208 a and the second magnetoresistance sensor 208 b, an outputvoltage is derived from a connecting point between the twomagnetoresistance elements. In other words, the output voltage is avoltage obtained by dividing a power supply voltage with the resistancesof the two magnetoresistance elements. The output voltage from the firstmagnetoresistance sensor 208 a is Vmr1 and the output voltage from thesecond magnetoresistance sensor 208 b is Vmr2.

In each of the first magnetoresistance sensor 208 a and the secondmagnetoresistance sensor 208 b, the spacing between the twomagnetoresistance elements is three fourth of a pitch between north andsouth poles formed in the magnet 207, that is, three fourth of thedistance between a pair of north pole and a south pole. The resistanceof a magnetoresistance element changes depending on the positionalrelationship between a magnetic field generated by the north and southpoles formed in the magnet 207 and the magnetoresistance element.Accordingly, the output voltage Vmr1 from the first magnetoresistancesensor 208 a and the output voltage Vmr2 from the secondmagnetoresistance sensor 208 b change.

FIGS. 3B, 4B, 5B, and 6B show the output voltage Vmr1 from the firstmagnetoresistance sensor 208 a and the output voltage Vmr2 from thesecond magnetoresistance sensor 208 b. The vertical axis representsvoltage and the horizontal axis represents the position of the secondfocus lens 203. The spacing between the first magnetoresistance sensor208 a and the second magnetoresistance sensor 208 b is determined suchthat the output voltage Vmr1 from the first magnetoresistance sensor 208a and the output voltage Vmr2 from the second magnetoresistance sensor208 b are shifted in phase by 90° with respect to each other. The lensCPU 201 can check a movement of the second focus lens 203 by observingthe output voltage Vmr1 from the first magnetoresistance sensor 208 aand the output voltage Vmr2 from the second magnetoresistance sensor 208b.

2-3. Autofocus Operation

The autofocus operation of the interchangeable lens 200 will bedescribed with reference to FIG. 2.

The camera body CPU 101 controls the interchangeable lens 200 such thatan optical signal collected by the interchangeable lens 200 is focusedonto the imaging device. Specifically, the camera body CPU 101 requeststhe lens CPU 201 to move the lens (S20).

According to the instruction from the camera body CPU 101, the lens CPU201 moves the first focus lens 202 and the second focus lens 203. In aresponse to the lens movement request, the lens CPU 201 sendsinformation indicating that the movement of the first focus lens 202 andthe second focus lens 203 is completed or that the first focus lens 202and the second focus lens 203 are moving, to the camera body CPU 101(S21).

The camera body CPU 101 requests lens state data from the lens CPU 201(S18). In a response to the request, the lens CPU 201 sends lens statedata including positional information of the first focus lens 202 andthe second focus lens 203, to the camera body CPU 101 (S19). Byrepeating the lens movement request (S20), the lens movement response(S21), the lens state data request (S18), and the lens state dataresponse (S19), the camera body CPU 101 controls the interchangeablelens 200 such that an optical signal collected by the interchangeablelens 200 is focused onto the imaging device.

2-4. Synchronizm Loss Detection Process

The operation to detect a loss of synchronizm of the second steppingmotor 205 will be described.

2-4-1. Synchronizm Loss Detection—Principle

The principle of detection of a loss of synchronizm of the secondstepping motor 205 using an output from the magnetoresistance sensor 208will be described.

FIGS. 7A to 7C are diagrams showing an output voltage from themagnetoresistance sensor 208. FIG. 7A is a diagram showing an outputvoltage from the magnetoresistance sensor 208 during the movement of thesecond focus lens 203. FIG. 7B is a diagram showing an output voltagefrom the magnetoresistance sensor 208 after the movement of the secondfocus lens 203 is stopped. FIG. 7C is a diagram showing an outputvoltage from the magnetoresistance sensor 208 when a loss of synchronizmoccurs in the second stepping motor 205 since an external shock isapplied to the second focus lens 203 after the movement of the secondfocus lens 203 is stopped. In all of the drawings, the horizontal axisrepresents time and the vertical axis represents voltage. An excitationphase of the second stepping motor 205 represented with numbers at thetop of FIGS. 7A to 7C. The second stepping motor 205 rotates 360° ineight steps.

As shown in FIG. 7A, during the movement of the second focus lens 203,both the output voltage Vmr1 from the first magnetoresistance sensor 208a and the output voltage Vmr2 from the second magnetoresistance sensor208 b change with eight steps of the excitation phase of the secondstepping motor 205 as one cycle. The output voltage Vmr1 from the firstmagnetoresistance sensor 208 a is shifted in phase by 90° from theoutput voltage Vmr2 from the second magnetoresistance sensor 208 b.

As shown in FIG. 7B, when the movement of the second focus lens 203 isstopped, both the output voltage Vmr1 from the first magnetoresistancesensor 208 a and the output voltage Vmr2 from the secondmagnetoresistance sensor 208 b hold their respective output voltagesobtained when the movement of the second focus lens 203 is stopped.

As shown in FIG. 7C, when a loss of synchronizm occurs in the secondstepping motor 205 since an external shock is applied to the secondfocus lens 203 after the movement of the second focus lens 203 isstopped, the output voltage Vmr1 from the first magnetoresistance sensor208 a and the output voltage Vmr2 from the second magnetoresistancesensor 208 b change. When the output voltage Vmr1 from the firstmagnetoresistance sensor 208 a and the output voltage Vmr2 from thesecond magnetoresistance sensor 208 b change from voltages obtained whenthe movement is stopped to voltages obtained when the excitation phaseof the second stepping motor 205 is shifted by two steps, the lens CPU201 detects that a loss of synchronizm occurs in the second steppingmotor 205.

With reference to FIG. 7C, the case is described in which an externalshock is applied to the second focus lens 203 after the movement of thesecond focus lens 203 is stopped, and thus a loss of synchronizm occursin the second stepping motor 205. However, even during the movement ofthe second focus lens 203, when the output voltage Vmr1 from the firstmagnetoresistance sensor 208 a and the output voltage Vmr2 from thesecond magnetoresistance sensor 208 b are shifted in an excitation phaseof the second stepping motor 205, by two steps of the phase, fromvoltages which are subsequently expected, the occurrence of a loss ofsynchronizm in the second stepping motor 205 can be detected.

2-4-2. Synchronizm Loss Detection—Flow

A synchronizm loss detection process will be described with reference toa flowchart in FIG. 8. FIG. 8 is a flowchart showing the process of thelens CPU 201 performed in a synchronizm loss detection process. In FIG.8 the “L” indicates the interchangeable lens 200 and the “B” indicatesthe camera body 100.

The lens CPU 201 compares the output voltage Vmr1 from the firstmagnetoresistance sensor 208 a and the output voltage Vmr2 from thesecond magnetoresistance sensor 208 b with their respective expectedvoltages (S1). If the voltage difference ΔX for at least one of thefirst magnetoresistance sensor 208 a and the second magnetoresistancesensor 208 b is greater than or equal to a threshold value, then thelens CPU 201 detects that a loss of synchronizm occurs in the secondstepping motor 205. The threshold value is set to a value equal to theamount of change in voltage for two steps of the excitation phase of thesecond stepping motor 205. On the other hand, if the voltage differencesΔX for both of the magnetoresistance sensors 208 a and 208 b are smallerthan the threshold value, then the lens CPU 201 determines that a lossof synchronizm does not occur in the second stepping motor 205.

When the lens CPU 201 determines that a loss of synchronizm does notoccur in the second stepping motor 205, the lens CPU 201 notifies thecamera body CPU 101 of the fact that the interchangeable lens 200 is ina steady state, through a lens movement response or a lens state dataresponse (S2). The camera body CPU 101 which is notified of the factthat the interchangeable lens 200 is in a steady state continues tocontrol the interchangeable lens 200.

On the other hand, when the lens CPU 201 detects that a loss ofsynchronizm occurs in the second stepping motor 205, the followingprocess is performed. First, the lens CPU 201 notifies the camera bodyCPU 101 of the fact that the interchangeable lens 200 is not in a steadystate, through a lens movement response or the lens state data response(S3). When the camera body CPU 101 is notified of the fact that theinterchangeable lens 200 is not in a steady state, the camera body CPU101 stops the control of the interchangeable lens 200 until it isnotified of the fact that the interchangeable lens 200 is in a steadystate.

The lens CPU 201 controls the drive circuit 209 to move the second focuslens 203 to its initial position (S4). The lens CPU 201 detects that thesecond focus lens 203 moves completely to its initial position, based onan output from the magnetoresistance sensor 208 (S5).

The lens CPU 201 controls the drive circuit 209 to move the first focuslens 202 to its initial position (S6). The lens CPU 201 detects that thefirst focus lens 202 moves completely to its initial position, based onan output from the photointerrupter 206 (S7).

When the first and second focus lenses 202 and 203 move to theirrespective initial positions completely, the lens CPU 201 controls thedrive circuit 209 to move the first and second focus lenses 202 and 203to their respective positions obtained immediately before the detectionof the loss of synchronizm (S8).

When the first and second focus lenses 202 and 203 move to theirrespective positions obtained immediately before the detection of theoccurrence of the loss of synchronizm, the lens CPU 201 notifies thecamera body CPU 101 of the fact that the interchangeable lens 200 is ina steady state, through the lens movement response or the lens statedata response (S9). When the camera body CPU 101 is notified of the factthat the interchangeable lens 200 is in a steady state, the camera bodyCPU 101 resumes the control of the interchangeable lens 200.

In short, when the interchangeable lens 200 detects a loss ofsynchronizm, the interchangeable lens 200 notifies the camera body 100of an unsteady state and stops receiving of instructions from the camerabody 100. During the movement of the first and second focus lenses 202and 203 to their respective initial positions, the interchangeable lens200 continues to stop receiving of instructions from the camera body100. Thereafter, when the first and second focus lenses 202 and 203 aremoved to their respective positions obtained immediately before thedetection of the loss of synchronizm, the interchangeable lens 200resumes receiving of instructions from the camera body 100.

3. Summary

As described above, an imaging apparatus system according to the presentembodiment includes the first and second focus lenses 202 and 203movable along an optical axis, the first and second stepping motors 204and 205 that drive the first and second focus lenses 202 and 203,respectively, and a magnetoresistance sensor 208 that detects a loss ofsynchronizm of one of the two stepping motors 204 and 205. One of thestepping motors that is provided with the magnetoresistance sensor 208is the second stepping motor 204 that drives the second focus lens 203which is the heaviest between the two lenses.

It is considered that a stepping motor that drives the heaviest movablelens is most likely to cause a loss of synchronizm when an externalshock is applied thereto. Hence, with the above configuration, detectionof a loss of synchronizm of a driver (stepping motor) for a lens that ismore likely to cause a loss of synchronizm can be performed, enabling todetect a loss of synchronizm with higher accuracy. In addition, sincethe heaviest lens is generally large and an optical influence exertedthereby is also large, reliably detecting a loss of synchronizm of theheaviest movable lens allows an optical adverse influence caused by aloss of synchronizm to be further reduced.

In addition, in general, resolution of a magnetoresistance sensor ishigher, by one digit, than resolution of a photointerrupter, and thususe of a magnetoresistance sensor as a synchronizm loss detector allowsdetection of a loss of synchronism to be performed with higher accuracy.

Other Embodiments

An imaging apparatus system according to one embodiment is describedabove. However, the concept of the above embodiment can be applied notonly to an imaging apparatus system including an interchangeable lensand a camera body but also to an imaging apparatus which a lens and acamera body are integrally formed. In this case, the imaging apparatusmay include both a lens CPU 201 (lens controller) and a camera body CPU101 (body controller) or one controller having both the function of thelens CPU 201 and the function of the body CPU 101.

The concept of the above embodiment can also be applied not only to animaging apparatus system or an imaging apparatus that includes twomovable lenses but also to an imaging apparatus system or an imagingapparatus that includes a plurality of (three or more) movable lenses.In this case, a loss of synchronizm of a stepping motor (driver) thatdrives the heaviest movable lens among the plurality of movable lensesis detected. This is because it is considered that a stepping motor thatdrives the heaviest movable lens is most likely to cause a loss ofsynchronizm when an external shock is applied thereto.

In the above embodiment, the lens CPU 201 detects a loss of synchronizmof the second stepping motor 205 and controls the drive circuit 209 tomove the second focus lens 203 to its initial position. However, thelens CPU 201 may detect a loss of synchronizm of the drive circuit 209and notify the camera body CPU 101 of the loss of synchronizm, and thecamera body CPU 101 may control the interchangeable lens 200 to move thesecond focus lens 203 to its initial position. Such control can also besimilarly applied to an imaging apparatus in which a lens and a camerabody are integrally formed, when the imaging apparatus includes a lensCPU 201 and a camera body CPU 101.

Although in the above embodiment the type of lens is a focus lens, theabove concept can also be applied to a zoom lens. Specifically, when theoptical system includes a plurality of lenses, a loss of synchronizm ofa driver (e.g., a stepping motor) that drives the heaviest lens in thelenses may be detected. This is because it is considered that a driverthat drives the heaviest movable lens is most likely to cause a loss ofsynchronizm when an external shock is applied thereto.

For example, when a zoom lens is composed of a plurality of lenses, aloss of synchronizm of a driver that drives the heaviest zoom lens maybe detected. Alternatively, when a plurality of lenses include a lenscomposing (serving as) a zoom lens and a lens composing (serving as) afocus lens, a loss of synchronizm of a driver that drives the heaviestlens between the lenses is detected. Alternatively, when the opticalsystem includes a plurality of lenses that have both the zoom functionand the focus function, a loss of synchronizm of a driver that drivesthe heaviest lens in all lenses may be detected.

INDUSTRIAL APPLICABILITY

The embodiment enables to detect a loss of synchronizm of a driver withhigh accuracy by means of a magnetoresistance sensor. Accordingly, theembodiment can be applied and is useful to an imaging apparatus system,such as a lens interchangeable digital camera, an imaging apparatus,such as a digital camera, and an interchangeable lens that composes animaging apparatus system.

What is claimed is:
 1. An imaging apparatus comprising: a plurality oflenses movable along an optical axis; a plurality of drivers configuredto drive the plurality of lenses, respectively; and a synchronizm lossdetector configured to detect a loss of synchronizm of one of theplurality of drivers, wherein the one of the plurality of drivers is adriver that drives a lens which is heaviest in the plurality of lenses.2. The imaging apparatus according to claim 1, wherein the plurality oflenses compose a focus lens.
 3. The imaging apparatus according to claim1, wherein the plurality of lenses compose a zoom lens.
 4. The imagingapparatus according to claim 1, wherein the plurality of lenses includea lens composing a zoom lens and a lens composing a focus lens.
 5. Theimaging apparatus according to claim 1, further comprising a controllerconfigured to control the plurality of drivers, wherein when thesynchronizm loss detector detects a loss of synchronizm, the controllercontrols the plurality of drivers to move the plurality of lenses totheir respective initial positions.
 6. The imaging apparatus accordingto claim 1, wherein the synchronizm loss detector is a magnetoresistancesensor.
 7. An interchangeable lens mountable to a camera body,comprising: a plurality of lenses movable along an optical axis; aplurality of drivers configured to drive the plurality of lenses,respectively; and a synchronizm loss detector configured to detect aloss of synchronizm of one of the plurality of drivers, wherein the oneof the plurality of drivers is a driver that drives a lens that isheaviest in the plurality of lenses.
 8. The interchangeable lensaccording to claim 7, wherein the plurality of lenses compose a focuslens.
 9. The interchangeable lens according to claim 7, wherein theplurality of lenses compose a zoom lens.
 10. The interchangeable lensaccording to claim 7, wherein the plurality of lenses include a lenscomposing a zoom lens and a lens composing a focus lens.
 11. Theinterchangeable lens according to claim 7, further comprising acontroller configured to control the plurality of drivers, wherein whenthe synchronizm loss detector detects a loss of synchronizm, thecontroller controls the plurality of drivers to move the plurality oflenses to their respective initial positions.
 12. The interchangeablelens according to claim 11, wherein the controller controls theplurality of drivers based on an instruction received from the camerabody, and stops receiving instructions from the camera body while theplurality of lenses are moving to their respective initial positionsbased on detection of a loss of synchronizm by the synchronizm lossdetector.
 13. The interchangeable lens according to claim 7, furthercomprising a controller configured to control the plurality of driversbased on an instruction received from the camera body, wherein thecontroller stops receiving instructions from the camera body when thesynchronizm loss detector detects a loss of synchronizm.
 14. Theinterchangeable lens according to claim 7, wherein the synchronizm lossdetector is a magnetoresistance sensor.